Rigged mesh deformed after opening blend file
As Firewill noted, it is a standard problem with python scripts. By default, Blender disables running scripts from scene, because downloaded scripts may contents malware.   

So, to run this scripts you mast press "Reload trusted" in header of window, to confirm that blender may trust scripts:



If for some reason, you haven't this buttons, there is a workaround: Open User Preferences, in File tab click auto run python scripts:



In this case it is recommended to add a downloads path as Excluded.